| 时间 | 值 （%） | 世界排名 |
|---|---|---|
| 2016 | 8.77 | 90 |
| 2015 | 8.48 | 90 |
| 2014 | 8.22 | 90 |
| 2013 | 7.98 | 90 |
| 2012 | 7.74 | 86 |
| 2011 | 7.53 | 84 |
| 2010 | 7.35 | 81 |
| 2009 | 7.29 | 80 |
| 2008 | 7.22 | 77 |
| 2007 | 7.1 | 77 |
| 2006 | 6.94 | 73 |
| 2005 | 6.76 | 70 |
| 2004 | 6.68 | 68 |
| 2003 | 6.61 | 67 |
| 2002 | 6.51 | 66 |
| 2001 | 6.38 | 59 |
| 2000 | 6.23 | 56 |
| 1999 | 6.21 | 56 |
| 1998 | 6.22 | 54 |
| 1997 | 6.24 | 56 |
| 1996 | 6.27 | 57 |
| 1995 | 6.27 | 59 |
| 1994 | 6.27 | 57 |
| 1993 | 6.26 | 55 |
| 1992 | 6.24 | 55 |
| 1991 | 6.22 | 54 |
| 1990 | 6.21 | 54 |
| 1989 | 6.25 | 57 |
| 1988 | 6.29 | 59 |
| 1987 | 6.34 | 63 |
| 1986 | 6.37 | 67 |